Method and system to prevent false restoration and protection in optical networks with a sliceable light source

ABSTRACT

A transport network, a node, and a method are disclosed. The transport network, the node, and the method detect a failure of a super channel originating from a sliceable light source that is routed through the transport network, by detecting an optical loss of signal by an optical power monitoring device, in presence or absence of an optical loss of signal of the complete band by at least one photo detector. This information is analyzed with a fault detection algorithm using a patch cable network configuration to determine a fault indication for a failure within the first node. The fault signal indicative of the fault indication is then passed to another node on the first path.

FIELD OF THE DISCLOSURE

The disclosure generally relates to methods and apparatuses forpreventing false restoration or protection in optical networks using acontroller at an add node that generates and sends at least one faultindication for a failure of super-channel originating from a sliceablelight source using an optical loss of signal detected by at least oneoptical power monitoring device, in combination or absence of an opticalloss of signal detected by a photo-detector and co-relating the samewith a local patch cable network configuration.

BACKGROUND

An Optical Transport Network (OTN) is comprised of a plurality of switchnodes linked together to form a network. The OTN includes a data layer,a digital layer, and an optical layer. The optical layer containsmultiple sub-layers. OTN structure, architecture, and modeling arefurther described in the International Telecommunication Unionrecommendations, including ITU-T G.709, ITU-T G.872, and ITU-T G.805,which are well known in the art. In general, the OTN is a combination ofthe benefits of SONET/SDH technology and dense wavelength-divisionmultiplexing (DWDM) technology (optics).

The construction and operation of switch nodes (also referred to as“nodes”) in the OTN is well known in the art. In general, the nodes ofan OTN are generally provided with a control module, input interface(s)and output interface(s). The control modules of the nodes in the OTNfunction together to aid in the control and management of the OTN. Thecontrol modules can run a variety of protocols for conducting thecontrol and management (i.e. Operation, Administration andMaintenance—referred to as OAM) of the OTN. One prominent protocol isreferred to in the art as Generalized Multiprotocol Label Switching(GMPLS).

Generalized Multiprotocol Label Switching (GMPLS) is a type of protocolwhich extends multiprotocol label switching (MPLS) to encompass networkschemes based upon time-division multiplexing (e.g. SONET/SDH, PDH,G.709), wavelength multiplexing, and spatial switching (e.g. incomingport or fiber to outgoing port or fiber). Multiplexing is when two ormore signals or bit streams are transferred over a common channel.

Wave-division multiplexing is a type of multiplexing in which two ormore optical carrier signals are multiplexed onto a single optical fiberby using different wavelengths (that is, colors) of laser light.

Generalized Multiprotocol Label Switching (GMPLS) includes multipletypes of label switched paths including protection and recoverymechanisms which specify (1) working connections within a network havingmultiple nodes and communication links for transmitting data between aheadend node and a tailend node; and (2) protecting connectionsspecifying a different group of nodes and/or communication links fortransmitting data between the headend node to the tailend node in theevent that one or more of the working connections fail. Workingconnections may also be referred to as working paths. Protectingconnections may also be referred to as recovery paths and/or protectingpaths and/or protection paths. A first node of a path may be referred toas a headend node or a source node. A last node of a path may bereferred to as a tailend node, end node or destination node. The headendnode or tailend node initially selects to receive data over the workingconnection and, if a working connection fails, the headend node ortailend node may select a protecting connection for passing data withinthe network. The set up and activation of the protecting connections maybe referred to as restoration or protection.

Lightpaths are optical connections carried over a wavelength, end toend, from a source node to a destination node in an optical transportnetwork (OTN). Typically, the lightpaths pass through intermediate linksand intermediate nodes in the OTN. At the intermediate nodes, thelightpaths may be routed and switched from one intermediate link toanother intermediate link. In some cases, lightpaths may be convertedfrom one wavelength to another wavelength at the intermediate nodes.

As previously mentioned, optical transport networks (OTN) have multiplelayers including a data packet layer, a digital layer, and an opticallayer (also referred to as a photonic layer). The data and digitallayers include an optical channel transport unit (OTU) sub-layer and anoptical channel data unit (ODU) sub-layer. The optical layer hasmultiple sub-layers, including the Optical Channel (OCh) layer, theOptical Multiplex Section (OMS) layer, and the Optical TransmissionSection (OTS) layer. The optical layer provides optical connections,also referred to as optical channels or lightpaths, to other layers,such as the electronic layer. The optical layer performs multiplefunctions, such as monitoring network performance, multiplexingwavelengths, and switching and routing wavelengths. The Optical Channel(OCh) layer manages end-to-end routing of the lightpaths through theoptical transport network (OTN). The Optical Multiplex Section (OMS)layer network provides the transport of optical channels through anoptical multiplex section trail between access points. The OpticalTransmission Section (OTS) layer network provides for the transport ofan optical multiplex section through an optical transmission sectiontrail between access points. The OCh layer, the OMS layer, and the OTSlayer have overhead which may be used for management purposes. Theoverhead may be transported in an Optical Supervisory Channel (OSC).

The Optical Supervisory Channel (OSC) is an additional wavelength thatis adapted to carry information about the network and may be used formanagement functions. The OSC is carried on a different wavelength thanwavelengths carrying actual data traffic. Typically, the OSC is usedhop-by-hop and is terminated and restarted at every node.

The International Telecommunications Union (ITU) recommendation ITU-TG.709 further defines the OTS, OMS and OCh layers and recommends use ofthe OSC to carry overhead corresponding to the layers. Additionally,ITU-T recommendation G.872 specifies defects for the OTS, OMS, and OChlayers as well as specifying Operation, Administration & Maintenance(OAM) requirements.

ITU-T recommendations suggest that the OSC utilize a SynchronousTransport Signal (STS) Optical Carrier transmission rate OC-3. OpticalCarrier transmission rates are a standardized set of specifications oftransmission bandwidth for digital signals that can be carried on fiberoptic networks. The OC-3 frame contains three column-interleaved STSLevel 1 (STS-1) frames; therefore, the line overhead consists of anarray of six rows by nine columns (that is, bytes). The OC-3 frameformat is further defined in Telecordia's Generic Requirements GR-253,“Synchronous Optical Network Common Generic Criteria,” Issue 4. The OC-3frame format contains a transport overhead portion. Within the transportoverhead portion, bytes designated as D4, D5, D6, D7, D8, D9, D10, D11,and D12 are defined by GR-253 for use by Data Communication Channel(DCC).

The patent application identified by U.S. Ser. No. 13/452,413, titled“OPTICAL LAYER STATUS EXCHANGE OVER OSC-OAM METHOD FOR ROADM NETWORKS”filed on Apr. 20, 2012, discloses methods for supporting OAM functionsfor the optical layers, for example, for carrying defect information andoverhead in the OSC. The application discloses methodology andapparatuses for supporting OAM functions such as continuity,connectivity, and signal quality supervision for optical layers. Themethodology discloses mapping optical layer overhead OAM information tospecific overhead bits and assigning the overhead bits to specific OSCoverhead bytes. This provides reliable exchange of overhead bytes overOSC between nodes.

There are many forms of failure indications, such as Open ConnectionIndication (OCI), Forward Defect Indication (FDI or FDI-P) and Lock(LCK). The network element determines which type of fault indication totransmit downstream. This can be accomplished by an optical supervisorychannel controller.

In a first level of fault processing, network elements conduct a localdetermination of optical signal integrity with inputs from various patchcabling points. This is accomplished with a local photodetector or anoptical power measuring device. The local determination results inanother form of signal known in the art as Optical Loss of Signal (OLOS)clear/declare. The results of the first level of processing (opticalpower monitor scanner) and its deduced fault indications (Port OLOS orSCH OLOS), are correlated and consolidated in a second level of faultprocessing. Based on the consolidation, a final deduced signalingindication is determined and sent downstream through the OpticalSupervisory Channel. The second level of processing is generallyrequired to distinguish whether there is a failure at the source(ROUTING card input) meaning that the optical path cannot be restored.In cases of failure at the source, a special Client Signal Failure (CSF)indication may also be sent downstream in the Optical SupervisoryChannel. This is required because unlike certain types of faultindications, such as FDI/OCI/LCK, a fault indication indicating a ClientSignal Failure means that the traffic cannot be restored. Thus, receiptof a Client Signal Failure indication by a downstream network elementdoes not result in a restoration or protection trigger. Client SignalFailure indications help in decision making taken by the restoration orprotection mechanism by isolating restorable failure cases fromnon-restorable failure cases (described in depth in detail in thefollowing sections). In case of failure conditions which manifest inClient Signal Failure, the failure is at the source itself and there isno alternate path available to restore the traffic. Hence, therestoration or protection mechanism will decide not to switch to analternate path in such cases.

Some network elements include a sliceable light source meaning that thelight source can source multiple super channels. Each super channel isformed of multiple distinct frequency bands that are then routedtogether. For the sliceable light sources, in the event that only one ofthe super channels has failed and is not sourcing enough power, suchfailure cannot be detected by the local photodiode as a complete loss ofoptical signal at band level is not there and only one of thesuper-channels has a failure but may be detected by a local opticalpower monitoring device. Further, the type of downstream signaling (FDIor CSF) is determined by an optical supervisory channel controller. Incertain cases, restorable failure scenarios (discussed in depth in alater section) result in downstream FDI signaling which causes therestoration and protection engines of downstream nodes to beginrestoration procedures. For non-restorable failure scenarios, CSF issignaled which will prevent the restoration and protection engines ofthe downstream nodes to take any action.

In light of the foregoing, there is a need to prevent false restorationin optical transport networks by detecting a failure at the source whenusing a sliceable light source. It is to such a system that detectsfailures at the source when using a sliceable light source that thepresent disclosure is directed.

SUMMARY

Methods and optical nodes are disclosed. The problems caused by falserestoration after a failure at the source has occurred with a sliceablelight source is fixed by detecting an optical loss of signal by anoptical power monitoring device within a multiplexer of an add node inpresence or absence of an optical loss of signal detected by aphoto-detector at an input port of the multiplexer, and co-relating thesame using a patch cable network configuration within the add node todetect a failure at the source (when appropriate) and generate an FDIand/or an client signal failure signal (CSF). The client signal failuresignal can be provided downstream in an optical supervisory channel toprevent false restoration due to a failure at the source.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate one or more implementationsdescribed herein and, together with the description, explain theseimplementations. In the drawings:

FIG. 1 is a partial illustration of an exemplary node within an opticaltransport network in accordance with the present disclosure describingconcepts within the optical transport network including services, fiberports/interfaces, an optical switch, and physical connections within theoptical switch directing data traffic from trail end point A to trailend point Z.

FIG. 2 is another partial illustration of the exemplary node in whichthe optical switch includes a multiplexer module configured to multiplexa group of super channels to an output port, referred to as a “bandport”. The multiplexer module of the optical switch includes powercontrol points to configure attenuation to control a launch power of thesuper channels at the band port.

FIG. 3 is a schematic view of an exemplary optical transport networkhaving an add node, an express node, and a drop node in accordance withexamples of the present disclosure.

FIG. 4 is a flow diagram of an exemplary optical transport networkhaving an add node, multiple express nodes, and a drop node where datatraffic is provided via a path from the add node, through the expressnodes to the drop node in accordance with the present disclosure.

FIG. 5 is a flow diagram of the exemplary optical transport network ofFIG. 4 where a fault has occurred between the add node and an expressnode, and where a restoration/protection path has been created betweenthe add node and the drop node.

FIG. 6 is a flow diagram of the exemplary optical transport network ofFIG. 4 where a fault (known as a failure at the source) has occurredwithin the add node in a location in which restoration or protection isin-effective since there is no alternate path available for the datatraffic.

FIG. 7 is a schematic diagram of the exemplary add node depicting achain of patch cable connections within the add node, and differentoutput ports that are known in the art as “degrees”.

FIG. 8 is another schematic diagram of the add node of FIG. 7 in which arestorable fault has occurred in a patch cable connecting a routing cardto one of a group of wavelength selective switches in the add node.

FIG. 9 is another schematic diagram of the add node of FIG. 7 in which anon-restorable fault (known as a failure at the source) has occurredbetween a light source and a routing card within the add node.

FIG. 10 is a schematic diagram of an exemplary add node having asliceable light source, and showing a super channel failure on thesliceable light source that is not detected by local photodiodes.

FIG. 11 is a flow chart of a fault detection algorithm that usesdifferent types of optical loss of signals and a local patch cablenetwork configuration to effectively solve the false restoration cases.

FIG. 12 is a partial block diagram of the add node in which an opticalsupervisory channel signaling controller is running the fault detectionalgorithm of FIG. 12 to convert an OLOS indication into a client signalfailure declare signal in accordance with the present disclosure.

DETAILED DESCRIPTION

The following detailed description refers to the accompanying drawings.The same reference numbers in different drawings may identify the sameor similar elements.

The problems caused by false restoration after a failure at the sourcehas occurred for a super-channel originating from a sliceable lightsource is fixed by detecting an optical loss of signal by an opticalpower monitoring device within a multiplexer of an add node withpresence or absence of an optical loss of signal being detected by aphoto-detector at an input port of the multiplexer, and using a patchcable network configuration within an add node to detect a failure atthe source (when appropriate) and generate an FDI and/or an clientsignal failure signal (CSF). The client signal failure signal can beprovided downstream in an optical supervisory channel to prevent falserestoration when a super channel originating from the sliceable lightsource has failed.

Definitions

If used throughout the description and the drawings, the following shortterms have the following meanings unless otherwise stated:

Band: The complete optical spectrum carried on the optical fiber.Depending on the fiber used and the supported spectrum which can becarried over long distances with the current technology, relevantexamples of the same are: C-Band/L-Band/Extended-C-Band.

Slice: In an N GHz (N=12.5, 6.25, 3.125) spaced frequency band of thewhole of the optical spectrum each such constituent band is called aslice. In one embodiment, a slice is the resolution at which the powerlevels can be measured by the optical monitoring device. The power levelbeing measured by the optical monitoring device represents the totaloptical power carried by the band represented by that slice. Asuper-channel pass-band is composed of a set of contiguous slices.

CSF: (Client Signal Fail)—is a signal sourced by the add node at thehead-end to signal the downstream nodes in an optical network that thereis a failure at the source. It is used to prevent false protection andrestoration.

FDI—Forward Defect Indication; and FDI-P (Forward Defect IndicationPath) are signals sent downstream as an indication that an upstreamdefect has been detected. This is similar to AIS (Alarm IndicationSignal) used in SONET/SDH.

OCI—Open Connection Indication is a signal to indicate that a particularOTN interface is not connected to an upstream signal.

LCK—Lock. It's a signal transmitted to the downstream to indicate thatthe traffic has been brought down intentionally by the user through someexternal command for some maintenance activity in the network.

LS (Light source): A card where the digital transport client ismapped/de-mapped to/from an optical channel. This is the place where theoptical channel originates/terminates. In the present disclosure, the LSmay be a sliceable light source configured to source multiple slices oflight simultaneously.

OAM (Operations Administration Maintenance): A standardized terminologyin transport networks used to monitor and manage the network.

OA (Optical Amplifier): A band control gain element generally EDFA orRAMAN based.

ODU—Optical Data Unit

OLDP (Optical Layer Defect Propagation): A fault propagation mechanismin the optical layer for OAM considerations and to facilitate protectionor restoration using the overhead frames mapped to an OSC.

OLOS—Optical Loss of Signal

OPM (Optical Power Monitor device): A device having a capability tomonitor power on a particular part of the spectrum on a per slice basis.

OSC (Optical Supervisory Channel): This is an additional wavelengthusually outside the amplification band (at 1510 nm, 1620 nm, 1310 nm oranother proprietary wavelength). The OSC carries information about themulti-wavelength optical signal as well as remote conditions at theoptical add/drop or OA sites. It is used for OAM in DWDM networks. It isthe multi-wavelength analogue to SON ET's DCC (or supervisory channel).

NMS—Network Management System

PD (Photodetector): A device which can measure the power levels in thecomplete band.

Power Control: The algorithm run in the power control domain to measurethe optical parameters and do the power adjustments to meet the targetpower level.

ROADM: Reconfigurable optical add drop multiplexer.

SCH (Super Channel/Optical Channel): A group of wavelengths sufficientlyspaced so as not to cause any interference among themselves which aresourced from a single light source including multiple lasers, each ofwhich supplying light at a corresponding wavelength, and managed as asingle grouped entity for routing and signaling in an optical network.

Sliceable Light Source: A light source originating multiplesuper-channels/optical channels.

WSS (Wavelength Selective Switch): A component used in opticalcommunications networks to route (switch) optical signals betweenoptical fibers on a per-slice basis. Generally power level controls canalso be done by the WSS by specifying an attenuation level on apass-band. The wavelength selective switch is a programmable devicewhere the source and destination fiber ports and associated attenuationcan be specified for a pass-band.

DESCRIPTION

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus. Further, unless expressly stated to the contrary,“or” refers to an inclusive or and not to an exclusive or. For example,a condition A or B is satisfied by anyone of the following: A is true(or present) and B is false (or not present), A is false (or notpresent) and B is true (or present), and both A and B are true (orpresent).

In addition, use of the “a” or “an” are employed to describe elementsand components of the embodiments herein. This is done merely forconvenience and to give a general sense of the inventive concept. Thisdescription should be read to include one or more and the singular alsoincludes the plural unless it is obvious that it is meant otherwise.

Throughout this application, the term “about” is used to indicate that avalue includes the inherent variation of error for the quantifyingdevice, the method being employed to determine the value, or thevariation that exists among the study subjects. For example, but not byway of limitation, when the term “about” is utilized, the designatedvalue may vary by plus or minus twelve percent, or eleven percent, orten percent, or nine percent, or eight percent, or seven percent, or sixpercent, or five percent, or four percent, or three percent, or twopercent, or one percent.

The use of the term “at least one” or “one or more” will be understoodto include one as well as any quantity more than one, including but notlimited to, 1, 2, 3, 4, 5, 10, 15, 20, 30, 40, 50, 100, etc. The term“at least one” or “one or more” may extend up to 100 or 1000 or moredepending on the term to which it is attached. In addition, thequantities of 100/1000 are not to be considered limiting, as lower orhigher limits may also produce satisfactory results.

In addition, the use of the phrase “at least one of X, V, and Z” will beunderstood to include X alone, V alone, and Z alone, as well as anycombination of X, V, and Z.

The use of ordinal number terminology (i.e., “first”, “second”, “third”,“fourth”, etc.) is solely for the purpose of differentiating between twoor more items and, unless explicitly stated otherwise, is not meant toimply any sequence or order or importance to one item over another orany order of addition.

As used herein, any reference to “one embodiment,” “an embodiment,”“some embodiments,” “one example,” “for example,” or “an example” meansthat a particular element, feature, structure, or characteristicdescribed in connection with the embodiment is included in at least oneembodiment. The appearance of the phrase “in some embodiments” or “oneexample” in various places in the specification is not necessarily allreferring to the same embodiment, for example.

In accordance with the present disclosure, messages, e.g., faultindications, transmitted between nodes can be processed by circuitrywithin the input interface(s), and/or the output interface(s) and/or anode controller, such as an optical supervisory channel controllerdiscussed below. Circuitry could be analog and/or digital, components,or one or more suitably programmed microprocessors and associatedhardware and software, or hardwired logic. Also, certain portions of theimplementations have been described as “components” that perform one ormore functions. The term “component,” may include hardware, such as aprocessor, an application specific integrated circuit (ASIC), or a fieldprogrammable gate array (FPGA), or a combination of hardware andsoftware. Software includes one or more computer executable instructionsthat when executed by one or more component cause the component toperform a specified function. It should be understood that thealgorithms described herein are stored on one or more non-transitorymemory. Exemplary non-transitory memory includes random access memory,read only memory, flash memory or the like. Such non-transitory memorycan be electrically based or optically based. Further, the messagesdescribed herein may be generated by the components and result invarious physical transformations. Additionally, it should be understoodthat the node can be implemented in a variety of manners as is wellknown in the art.

Referring now to the drawings, and in particular to FIG. 1, showntherein is a partial schematic diagram of a node 10 constructed inaccordance with the present disclosure providing services 12A and 12B ina transport network 14. To assist in providing the service 12A, the node10 is configured to transport data from trailend point ‘A’ to trailendpoint T. The transport network may conform to the requirements set forthas per the definitions of ITU-T G.705 for transport networkarchitectural components.

As will be discussed in more detail below, the node 10 is adapted tofacilitate the communication of data (which may be referred to herein as“traffic”) between multiple nodes 10 in the transport network 14. Thenode 10 is provided with one or more input interfaces 16 (three inputinterfaces 16A, 16B, and 16C being depicted in FIG. 1 by way ofexample), one or more output interfaces 18 (three output interfaces 18A,18B, and 18C being depicted in FIG. 1 by way of example), a controlmodule 20, and an optical switch 22. The input interfaces 16 are alsoreferred to herein as a tributary input port, or ingress port. Theoutput interfaces 18 are also referred to herein as tributary outputport or egress port.

In general, the input interfaces 16A, 16B, and 16C are adapted toreceive traffic from the transport network 14, and the output interfaces18A, 18B, and 18C are adapted to transmit traffic onto the transportnetwork 14. The optical switch 22 serves to communicate the traffic fromthe input interface(s) 16A, 16B, and 16C, to the output interface(s)18A, 18B, and 18C to provide the services 12A and 12B, for example. And,the control module 20 serves to control the operations of the inputinterfaces 16A, 16B, and 16C, the output interfaces 18A, 18B, and 18C,and the switch 22.

The control module 20 may run GMPLS and can be referred to herein as a“control plane.” The control plane may use GMPLS protocols to setup oneor more working paths and one or more protecting paths during anegotiation. During the negotiation between the control planes of thenodes 10 within the transport network 14, labels may be allocated forin-band signaling as part of the GMPLS processing, for example, as willbe appreciated by persons of ordinary skill in the art having thebenefit of the instant disclosure.

The node 10 can be implemented in a variety of manners, includingcommercial installations having one or more backplanes (not shown),racks, and the like. In this example, the input interfaces 16, theoutput interfaces 18, the control module 20 and the switch 22 aretypically implemented as separate devices, which may have their ownpower supply, local memory and processing equipment. In another example,the node 10 can be implemented as a single device having a shared powersupply, memory and processing equipment. Or, in another example, thenode 10 can be implemented in a modular manner in which the inputinterfaces 16, the output interfaces 18, the control module 20 and theswitch 22 share a power supply and/or housing.

The input interfaces 16, and the output interfaces 18 of one node 10 areadapted to communicate with corresponding input interfaces 16, andoutput interfaces 18 of another node 10 within the transport network 14via communication links 30A, 30B, 30C, and 30D (as shown in FIG. 1). Thecommunication links 30A, 30B, 30C, and 30D may be fiber optic cables. Anexample of the input interface 16 and/or the output interface 18 is anEthernet card or optical port. In general, each of the input interfaces16 and/or the output interfaces 18 may have a unique logicalidentification, such as an IP address. The implementation of the inputinterfaces 16, and the output interfaces 18 will depend upon theparticular type of communication link 30A, 30B, 30C, and 30D that theparticular input interface 16 and/or output interface 18 is designed tocommunicate with.

In accordance with the present disclosure, messages transmitted betweenthe nodes 10, can be processed by circuitry within the inputinterface(s) 16, and/or the output interface(s) 18 and/or the controlmodule 20. Circuitry could be analog and/or digital, components, or oneor more suitably programmed microprocessors and associated hardware andsoftware, or hardwired logic. Also, certain portions of theimplementations have been described as “components” that perform one ormore functions. The term “component,” may include hardware, such as aprocessor, an application specific integrated circuit (ASIC), or a fieldprogrammable gate array (FPGA), or a combination of hardware andsoftware. Software includes one or more computer executable instructionsthat when executed by one or more component cause the component toperform a specified function. It should be understood that thealgorithms described herein are stored on one or more non-transient ornon-transitory memory. Exemplary non-transitory memory includes randomaccess memory, read only memory, flash memory or the like. Suchnon-transitory memory can be electrically based or optically based.Further, the messages described herein may be generated by thecomponents and result in various physical transformations.

As discussed above, transport network elements, e.g., the node 10,involve service provisioning through a north bound entity—NMS or GMPLSor some other distributed control plane mechanism handling dynamicservice provisioning. A service provisioning involves association of twotrails as end-points which can be implemented by configuring the opticalswitch 22 through device settings in the connection fabric. In thetransport network 14, the trail entity involved may be a super-channelwhich is a part of the optical spectrum which carries the digitaltransport client information converted into light spanning a particularspectrum through some kind of modulation. The optical switch 22 can beimplemented as a wavelength selective switch, or in some cases a MCSdevice.

FIG. 2 depicts an optical device 31, e.g., a card, which is configuredto multiplex groups of optical signals (referred to herein assuper-channels) provided by the input interfaces 16A, 16B, and 16C tothe output interface 18A. The optical device 31 may be implemented asthe optical switch 22, which in this example can be a wavelengthselective switch 32 having a control device 34 with power control points36A, 36B, and 36C. The power control points 36A, 36B, and 36C are usedto control the light eventually being launched onto the output interface18 (which is referred to in this example as the “band port.” The opticaldevice 31 is also provided with a power monitoring device 38. Ingeneral, the control device 34 includes an automatic control loopmechanism to account for losses, equipment aging and change of power atthe source.

In modules where the optical switch 22 is the wavelength selectiveswitch 32 used to make associations across the input interfaces 16 andthe output interface 18, e.g., the band ports, the same wavelengthselective switch 32 provides an option (implemented via the powercontrol points 36A, 36B, and 36C and monitored by the power monitoringdevice 38) to configure attenuation to control the launch power of theoptical signals, e.g., the super-channel. Hence, the fabric and thepower control points 36 are parts of the same wavelength selectiveswitch 32. It is still possible in other types of optical switch 22modules with some other kind of fabric where the fabric is just used tomake associations across the input interfaces 16 and the outputinterfaces 18 but the super-channel power controls is done through someother device, for example—a VOA. The current disclosure does not limitthe disclosure to any particular kind of optical switch 22 and istherefore intended to cover all such possible optical switch fabricarchitectures. To facilitate power controls the power monitoring device38 can be used.

For the purpose of fault isolation in the transport network 14 andtriggers facilitating protection and restoration, defect signalingcarried in some in-band or out-band overhead is needed. One of the mostimportant features of any transport network 14, i.e., the OAM, isfacilitated through in-band or out-band overhead. In case of thetransport network 14, the various fault triggers are OCI, FDI, and CSF,preferably carried in the in-band frame bytes.

As per the definition in OTN specification, OCI is sourced when theconnection is absent in the fabric, AIS/FDI in case of upstream failuresto indicate to the downstream that some fault has occurred.

In case of the node 10 having the optical switch 22 (such as DWDMequipment with an optical fabric), the various fault triggers are OCI,FDI (similar to AIS), and CSF carried in the OSC.

Referring to FIG. 3, shown therein is an example of the transportnetwork 14. In this example, the transport network 14 includes threenodes 10 that are labeled in FIG. 3 with the notations 10A, 10B, and 10Cfor purposes of clarity. Node 10A is an add node having multiple lightsources 50A and 50B, and the optical switch 22 is configured as amultiplexer. Node 10B is an express node having the optical switch 22implemented as a demultiplexer/multiplexer pair; a light source 52; anda light sink 54. Node 10C is a drop node having the optical switch 22implemented as a demultiplexer; and multiple light sinks 56A and 56B.The multiplexer/demultiplexer can comprise of colorless wavelengthselective switches as a muxing/demuxing device or colored passivemuxes/demuxes or may simply involve a junction point to which multiplelight sources/sink are connected. The nodes 10A and 10B may also includea routing card 60 (see FIG. 10) which may be directly connected to thelight source(s) 50A and/or 50B, and the light sink(s) 56A and/or 56B.The routing card 60 facilitates switching and bridging of the lightsource(s) 50/light sink(s) 56 to different degrees which may be used forpurpose of restoration. The routing card 60 may include an MCS device orsimply may be a broadcast module.

Shown in FIG. 4 is another example of the transport network 14, havingnodes 10 labeled for purposes of clarity as 10A, 10B1, 10B2, 10B3, 10B4,10B5, and 10C. In this example, the node 10A is the add node; the nodes10B1, 10B2, 10B3, 10B4, 10B5 are express nodes, and node 10C is a dropnode. Also shown in FIG. 4 is a lightpath 90 providing a service fromthe add node 10A to the drop node 10C. As discussed herein, a lightpathis a connection between two nodes 10 in the transport network 14, and isset up by assigning a dedicated wavelength on each link in thelightpath. In this case, the lightpath 90 provides an optical servicefrom the light source 52 of the node 10A to the light sink 54 of thenode 10C, and vice-versa. The optical layer multiplexes multiplelightpaths into a single fiber and allows individual lightpaths to beextracted efficiently from the composite multiplex signal at node 10C,for example. This lightpath can be set up or taken down in response to arequest. The transport network 14 may include any number of opticalnodes 10. Further, the transport network 14 may be configured in anytopology, for example, linear, ring, or mesh.

For purposes of simplicity of explanation, communication links 92A-92Jare illustrated in FIG. 4, but it will be understood that there may bemore or fewer communication links 92.

The optical nodes 10 are adapted to facilitate the communication of datatraffic (which may be referred to herein as “traffic” and/or “data”) inthe transport network 14 over communication links 92A-92J, as well asinto and out of the transport network 14.

The communication links 92 can be implemented in a variety of ways, suchas an optical fiber or other waveguide carrying capabilities. Thecommunication links 92 can be fiber optic cables. Some of thecommunication links 92 can be implemented as patch cables, such as thecommunication links 92A and 92G.

FIG. 5 shows a failure occurring in the transport network 14 in thecommunication link 92B, and an alternate restore/protect path 100 beingset up for the optical service when a failure happened on the previouslightpath 90. As shown in FIG. 5, the lightpath 90 has been disabled.

FIG. 6 shows a failure scenario in the transport network 14 in thecommunication link 92A where restoration or protection is in-effectivesince there is no alternate path available for the traffic flow. Suchkinds of failure are referred to as failure at the source.

FIG. 7 is a block diagram of part of the add node 10A in which the lightsource 52 is connected to the routing card 60 with a first patch cable104. The routing card 60 is connected to a first MUX/OSC card 71A via asecond patch cable 106, and is also connected to a second MUX/OSC card71B via a third patch cable 108. The line out towards network for thefirst MUX/OSC card 71A is referred to in FIG. 7 as DEGREE 1; and theline out towards network for the second MUX/OSC card 71B is referred toin FIG. 7 as DEGREE 2.

FIG. 8 is another block diagram of the part of the add node 10A depictedin FIG. 7 showing an exemplary patch cable failure in the patch cable106 which manifests in downstream FDI signaling.

FIG. 9 is another block diagram of the part of the add node 10A depictedin FIG. 10 showing another exemplary patch cable failure scenario in thepatch cable 104 which manifests as downstream CSF signaling. Thiscondition is referred to as failure at the source.

FIG. 10 is another block diagram of the add node 10A having a sliceablelight source 120 generating multiple super channels and providing themultiple super channels to the routing card 60 via the patch cable 104.In this embodiment, the add node 10A include a first series of cascadedmultiplexers 124A-124B, and a second series of cascaded multiplexers126A-126B. The routing card 60 is connected to an input port of themultiplexer 124A via the second patch cable 106, and is also connectedto an input port of the multiplexer 126A via a third patch cable 108. Anoutput port of the multiplexer 124A is connected to an input port of themultiplexer 124B via a fourth patch cable 130. An output port of themultiplexer 126A is connected to an input port of the multiplexer 126Bvia a fifth path cable 132. The add node 10A can be provided withadditional multiplexers and patch cables to multiplex furtherslices/super channels into the MUX/OSC cards 71A or 71B. In any event,the routing card 60 includes a photodetector 128 placed at the inputport of the routing card 60 to determine the presence or absence of thesuper channels and to output a signal indicative of an optical loss ofsignal in the absence of the super channels. The multiplexers 124A,124B, 126A, and 126B also include a photodector 130A, 130B, 132A, 132Bthat are also placed at the input port to determine the presence orabsence of the super channels and to output a signal indicative of anoptical loss of signal in the absence of the entire band, includingthose slices occupied by the super channels. The multiplexers 124A,124B, 126A, and 126B also include an optical power monitoring device134A, 134B, 136A, 136B that measure optical power on a per slice basisto determine the presence or absence light on particular slices withinthe super channels and to output a signal indicative of an optical lossof signal in the absence of light on one or more slices within the superchannels.

The sliceable light source 120 originates multiple wavelengths inC/Extended-C/L band, composing multiple super channels, directed towarddifferent destinations using the routing and/or broadcastingmultiplexers 124A, 124B, 126A, and 126B, and MUX/OSC cards 71A and 71B.

Each of the optical power monitoring devices 134A, 134B, 136A, and 136Bindicates OLOS raise and clear condition for a super channel and sendsthe OLOS raise and clear condition to the OSC signaling controller 140,that executes the fault detection algorithm and decides on the signalingindication (OCI/FDI/LCK/CSF) to be sent to an OSC signaling transmitter142 to trigger restoration in the downstream protection and recoveryengines. In FIG. 12, the optical power monitoring device 134B, the OSCsignaling controller 140, and the OSC signaling transmitter 142 arehosted on the same card. In another implementation, it may be possibleto have the optical power monitoring device 134B, the OSC signalingcontroller 140, and the OSC signaling transmitter 142 hosted indifferent cards. In such cases, the flow of signaling indication SCHOLOS from the optical power monitoring device 134B, to the OSC signalingcontroller 140 will be done through an inter-card control planemessaging as designated by a reference numeral 144, and shown in FIG. 12rather than the currently shown intra-card control plane messaging.

The optical power monitoring device 134B may also send optical controlloop messages to be mapped to some part of the digital frame formed bythe OSC signaling transmitter 142 to be sent to downstream nodes 10B and10C for control loop purpose. This is not shown in the current diagramas the same can also be sent through some other interface to thedownstream nodes 10B and 10C. The super channels from the sliceablelight source 120 are multiplexed and transported in the transportnetwork 14.

The routing card 60 facilitates switching and bridging of the lightsource/sink to different degrees, used for purpose of restoration. Abase device in a routing card may be an MCS device or simply may be abroadcast module.

The multiplexers 124A, 124B, 126A, and 126B may comprise one or moreWSS, or may simply involve a junction point to which multiple lightsources/sink are connected.

The present disclosure provides a solution to prevent false restorationfor any failed super channel, which is sourced from the sliceable lightsource 120. The sliceable light source 120 is associated with therouting card 60 that can independently route a super channel alongdifferent paths. The cascaded multiplexers 124A and 124B, and 126A and126B, for example, are preferably within the same node 10A as thesliceable light source 120 and the routing card 60.

As discussed above, the photodetectors 128, 130A, 130B, 132A, and 132B,for example, cannot detect failure of a particular super channel sourcedfrom the sliceable light source 120, as the photodetectors 128, 130A,130B, 132A, and 132B will not detect complete optical loss of light dueto multiple super channels being incident on the photodetectors 128,130A, 130B, 132A, and 132B.

A particular failed slice within the super channel or carrier level OLOScan be detected by the optical power monitoring devices 134A, 134B,136A, and 136B. This failure for a particular super channel can act as arestoration trigger. By knowing photodetector and optical powermonitoring device locations within a patch cable network configurationof the add node 10A, correlating photodetector detected signals (e.g.,sufficient light, or optical loss of light) and optical power monitoringdevice reported failure, such false restorations can be avoided inaccordance with the present disclosure.

FIG. 11 is a flow chart of a fault detection algorithm 160 that can berun by the OSC signaling controller 140 that uses an optical loss ofsignal detected by at least one of the optical power monitoring devices134A, 134B, 136A, and 136B, during the absence of an optical loss ofsignal being detected by the photo-detectors 128, 130A, 130B, 132A, and132B, and a patch cable network configuration of the add node 10A toeffectively solve the false restoration cases. The physical locations ofthe optical power monitoring devices 134A, 134B, 136A, and 136B, and thephoto-detectors 128, 130A, 130B, 132A, and 132B are known and can bestored in a patch cable topology database 161 by a management layer andobtained when associations between cards is accomplished. At a step 162,the fault detection algorithm 160 receives data indicative of a scan bythe optical power monitoring devices 134A, 134B, 136A, and 136B. Thefault detection algorithm 160 then branches to a step 164 to analyze thedata and determine whether or not any of the optical power monitoringdevices 134A, 134B, 136A, and 136B is detecting an optical loss ofsignal. If not, the fault detection algorithm branches back to the step162 to receive subsequent data from the optical power monitoring devices134A, 134B, 136A, and 136B.

If the fault detection algorithm 160 determines that any of the opticalpower monitoring devices 134A, 134B, 136A, and 136B is detecting anoptical loss of signal, the fault detection algorithm branches to a step166 to determine whether an input tributary port of the routing card 60is detecting an optical loss of signal. This can be determined byanalyzing an output of the photodetector 128 located incident to thetributary port of the routing card 60. If the photodetector 128 isindicating an optical loss of signal, the fault detection algorithm 160determines the presence of a failure at the source, and branches to astep 168 to insert the CSF enable signal to the OSC transmitter 142. Ifthe input tributary port of the routing card 60 is indicating sufficientpower (i.e., not in an optical loss of signal condition), the faultdetection algorithm 160 branches to a step 170 to determine whether ornot a failure at the source is occurring by analyzing the patch cablenetwork configuration of the add node 10A to determine where the faultis being detected relative to the patch cables 106, 108, 130, 132,routing card 60, and multiplexers 124A, 124B, 126A, and 126B. Inparticular, the fault detection algorithm 160 determines whether or notthe optical power monitoring device reporting the optical loss of signalis next to the routing card 60, i.e., the optical power monitoringdevice 134A, or 136A. If not, a failure at the source does not exist,and the fault detection algorithm branches to a step 172 to provide anFDI signal, for example, to the OSC transmitter 142. If the opticalpower monitoring device reporting the optical loss of signal is next tothe routing card 60, then the fault detection algorithm 160 branches toa step 174 to determine whether the photodetector 130A, or 132A incidentto the tributary input port of the multiplexer 124A or 126A is alsoreporting an optical loss of signal. If so, the fault detectionalgorithm 160 determines that a failure at the source does not exist,and branches to a step 176 to report an FDI to the OSC signalingcontroller 140. If the fault detection algorithm 160 determines at thestep 174 that the photodetector 130A, or 132A incident to the tributaryinput port of the multiplexer 124A or 126A is not reporting an opticalloss of signal, then the fault detection algorithm 160 concludes thatone or more of the slices of the sliceable light source 120 has failed,and declares a failure at the source. The fault detection algorithm 160then branches to the step 168 to insert the CSF enable to the OSCtransmitter 142.

FIG. 12 is a partial block diagram of the add node 10A in which theoptical supervisory channel signaling controller 140 is running thefault detection algorithm 160 of FIG. 11 to convert a superchanneloptical loss of signal detected by an optical power monitoring device124B into an FDI indication or a client signal failure declare signal inaccordance with the present disclosure. As shown, the node 10A includesthe patch cable network topology database 161 that includes anon-transitory computer readable medium that stores informationindicative of order and location of the various components in the addnode 10A, including the order and location of the routing card 60, themultiplexers 124A, 124B, 126A, and 126B, the optical power monitoringdevices 134A, 134B, 136A, 136B, and the photo detectors 128. When asignal from one of the components is received by the OSC signalingcontroller 140, the OSC signaling controller 140 correlates the signalwith the information within the patch cable network topology database160 to determine the location of the component within the networktopology of the add node 10A.

CONCLUSION

The problems caused by false restoration after a failure of a superchannel at the source has occurred with a sliceable light sourcesourcing multiple super-channels simultaneously is fixed by monitoring(a) optical power monitoring devices for an optical loss of signal, and(b) photodetectors for sufficient light or optical loss of signal duringa time period in which at least one of the optical power monitoringdevices is detecting an optical loss of signal of only a portion of thebands, and (c) network topology information (including patch cablenetwork configuration) within an add node to detect a failure at thesource (when appropriate) and generate an FDI or a client signal failuresignal. The client signal failure signal can be provided downstream inan optical supervisory channel to prevent false restoration of a failureat the source when the sliceable light source has failed.

The foregoing description provides illustration and description, but isnot intended to be exhaustive or to limit the inventive concepts to theprecise form disclosed. Modifications and variations are possible inlight of the above teachings or may be acquired from practice of themethodologies set forth in the present disclosure.

Also, certain portions of the implementations may have been described as“components” or “circuitry” that performs one or more functions. Theterm “component” or “circuitry” may include hardware, such as aprocessor, an application specific integrated circuit (ASIC), or a fieldprogrammable gate array (FPGA), or a combination of hardware andsoftware.

Even though particular combinations of features are recited in theclaims and/or disclosed in the specification, these combinations are notintended to limit the disclosure. In fact, many of these features may becombined in ways not specifically recited in the claims and/or disclosedin the specification. Although each dependent claim listed below maydirectly depend on only one other claim, the disclosure includes eachdependent claim in combination with every other claim in the claim set.

No element, act, or instruction used in the present application shouldbe construed as critical or essential to the invention unless explicitlydescribed as such outside of the preferred embodiment. Further, thephrase “based on” is intended to mean “based, at least in part, on”unless explicitly stated otherwise.

What is claimed is:
 1. A method comprising the steps of: receiving, bycircuitry of a controller of a first node on a first path within atransport network, a first signal indicating an optical loss of signalgenerated by an optical power monitoring device, and a second signalgenerated by at least one photo detector, the first node having arouting card and a series of cascaded multiplexers connected to therouting card with patch cables, the optical power monitoring devicebeing a first component within at least one of the multiplexers, thephoto detector being a second component of at least one of the routingcard and the multiplexers; determining a first location of the opticalpower monitoring device within a patch cable network configuration ofthe first node; determining a second location of the photo-detectorwithin the patch cable network configuration of the first node;analyzing the first and second signals with the patch cable networkconfiguration of the first node and the first and second locations todetermine at least one fault indication for a failure within the firstnode; and passing a fault signal indicative of the at least one faultindication to a second node on the first path.
 2. The method of claim 1,wherein the controller is an optical supervisory channel controller. 3.The method of claim 1, wherein the fault signal is selected from a groupconsisting of a forward defect indication signal, an open connectionindication signal, a lock signal, and a client signal failure signal. 4.The method of claim 3, wherein the client signal failure signal isindicative of a failure at the source.
 5. The method of claim 1, whereinthe first node is an add node.
 6. The method of claim 1, wherein theoptical loss of signal is a first optical loss of signal, and whereinthe photo detector is part of the routing card, and is indicative of asecond optical loss of signal, and wherein in the step of analyzing thefirst and second signals with the patch cable network configuration ofthe first node, the controller determines that the fault signal includesa client signal failure signal based upon the second signal indicatingthat the photo detector is part of the routing card, and the secondoptical loss of signal.
 7. The method of claim 1, wherein the opticalpower monitoring device and the photo detector is a part of a firstmultiplexer of the cascaded multiplexers, the first multiplexer beinglocated adjacent to the routing card, and wherein in the step ofanalyzing the first and second signals with the patch cable networkconfiguration of the first node, the controller determines that thefault signal includes a client signal failure signal based upon anabsence of the photo detector generating an optical loss of signal.
 8. Anode, comprising: a sliceable light source generating multiplewavelengths of light composing multiple super channels, each of thesuper channels being a group of the wavelengths that are routed togetherthrough the first path; a routing card having a first input port, afirst photo detector at the first input port, and an output port, thefirst input port receiving the light and directing the multiple superchannels of light composing the light of the super channel to the outputport, the first photo detector generating a first signal indicative ofonly one of a presence or absence of the light of the super channels; amultiplexer having a second input port receiving the light of one ormore super channel from the routing card, a second photo detector at thesecond input port; and an optical power monitoring device, the opticalpower monitoring device receiving light of the one or more superchannel, measuring the light on a per band basis, and detecting anoptical loss of signal within the one or more super channel, the opticalpower monitoring device generating a second signal indicative of theoptical loss of signal, the second photo detector generating a thirdsignal indicative of only one of a presence or absence of the light ofthe one or more super channel; and a first patch cable connecting thesliceable light source to the first input port of the routing card; asecond patch cable connecting the output port of the routing card to thesecond input port of the multiplexer; and a controller having circuitryexecuting a fault detection algorithm that receives the first signal,the second signal, and the third signal, receives information indicativeof a patch cable network configuration of the first and second patchcables, and determines whether the optical loss of signal detected bythe optical power monitoring device is a failure at the source.
 9. Thenode of claim 8, wherein the fault detection algorithm determines thatthe optical loss of signal detected by the optical power monitoringdevice is the failure at the source by based upon the first signalindicating that the first photo detector is part of the routing card,and the first signal indicating the absence of the light of the superchannels.
 10. The node of claim 8, wherein the fault detection algorithmdetermines that the optical loss of signal detected by the optical powermonitoring device is the failure at the source based upon the thirdsignal being indicative of the presence of the light of the one or moresuper channel.
 11. The node of claim 8, wherein the fault detectionalgorithm determines that the multiplexer is associated next to therouting card, and the third signal being indicative of the presence ofthe light of the one or more super channel.
 12. A transport network,comprising: a first node; a second node; an optical fiber connecting thefirst node to the second node, the optical fiber having an opticalsupervisory channel; wherein the first node comprises: a sliceable lightsource generating multiple wavelengths of light composing multiple superchannels, each of the super channels being a group of the wavelengthsthat are routed together through the first path; a routing card having afirst input port, a first photo detector at the first input port, and anoutput port, the first input port receiving the light and directing themultiple wavelengths of light composing the light of the super channelsto the output port, the first photo detector generating a first signalindicative of only one of a presence or absence of the light of thesuper channels; a multiplexer having a second input port receiving thelight of the one or more super channel from the routing card, a secondphoto detector at the second input port; and an optical power monitoringdevice, the optical power monitoring device receiving light of the oneor more super channel, measuring the light on a per band basis, anddetecting an optical loss of signal within the super channel, theoptical power monitoring device generating a second signal indicative ofthe optical loss of signal, the second photo detector generating a thirdsignal indicative of only one of a presence or absence of the light ofthe one or more super channel; and a first patch cable connecting thesliceable light source to the first input port of the routing card; asecond patch cable connecting the output port of the routing card to thesecond input port of the multiplexer; and a controller having circuitryexecuting a fault detection algorithm that receives the first signal,the second signal, and the third signal, receives information indicativeof a patch cable network configuration of the first and second patchcables, and determines whether the optical loss of signal detected bythe optical power monitoring device is a failure at the source; and anoptical supervisory channel transmitter receiving a signal indicative ofthe failure at the source, and inserting a client signal failure signalonto the optical supervisory channel of the optical fiber.
 13. Thetransport network of claim 12, wherein the fault detection algorithmdetermines that the optical loss of signal detected by the optical powermonitoring device is the failure at the source by based upon the firstsignal indicating that the first photo detector is part of the routingcard, and the first signal indicating the absence of the light of theone or more super channel.
 14. The transport network of claim 12,wherein the fault detection algorithm determines that the optical lossof signal detected by the optical power monitoring device is the failureat the source based upon the third signal being indicative of thepresence of the light of the one or more super channel.
 15. Thetransport network of claim 12, wherein the fault detection algorithmdetermines that the multiplexer is associated next to the routing card,and the third signal being indicative of the presence of the light ofthe one or more super channel.